Convert character to unsigned type because isprint doesn't understand negative characters.
Convert character to unsigned type because isprint doesn't understand negative characters.

This leads to assertion failure in browser dso test when using debugging version of the plugin in windows 64-bit.

BUG= http://code.google.com/p/nativeclient/issues/detail?id=1845
TEST= dynamic_library_browser_test in windows 64-bit.
Review URL: http://codereview.chromium.org/7074007

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@5480 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client,nacl-webkit/native_client,sbc100/native_client